This invention relates to solar energy collection, and is more particular directed towards an arrangement for attaching solar modules to a supporting structure, such as a roof, rack or tracking structure. The invention is more particularly directed to improvements in hardware clips that facilitate the attachment of unframed photovoltaic modules on any of a variety of supporting structures, for the purpose of constructing arrays of photovoltaic modules in a system to produce electricity. The invention may be employed for the attachment of solar thermal panels and non-solar panels as well.
Photovoltaic systems are used for a variety of purposes, including for use as a utility interactive power supply, as a power supply for remote radiotelephone station, or to power an unattended monitoring station, for example.
Photovoltaic systems consist of one or more photovoltaic (PV) modules, arranged in arrays, attached to a supporting surface, and interconnected with electrical wiring to switches, inverters, battery chargers and batteries, etc. This invention relates to a novel method for attaching the PV modules to a variety of supporting structures. PV modules typically consist of a PV laminate and they may also include a frame. The PV laminate typically consists of an assembly of crystalline or amorphous semiconductor devices electrically interconnected and encapsulated between a transparent front cover of glass or plastic and a back cover. Also, a PV module typically includes electrical conductors exiting the laminate edge or back cover which conduct the solar generated current through the electrical circuit including the PV module. The back cover is typically a tough insulating material that is an electrical insulator, is impervious to moisture, and is often made of either flexible Tedlar and/or other foil, film or rigid glass or plastic.
For PV modules that incorporate a frame, the frame often consists of multiple aluminum extrusion elements which are assembled to surround the laminate, and are mechanically interconnected at the module corners. The frame sections often include a channel to capture the laminate, which channel often is filled with a sealant during the frame assembly procedure. The sealant, often a butyl compound in the form of a gunable caulk, tape or putty, acts to promote the sealing of the edge of the laminate, to provide an adhesive attachment between the frame and the laminate, and to provide a cushion to protect the laminate edge from mechanical damage.
For PV modules that incorporate frames, those frames typically include holes which may accommodate fasteners for the attachment of the PV module to a supporting surface. In this way, the PV module may be attached to a variety of supporting structures, including a tracking structure described in U.S. Pat. No. 6,058,930, or attached onto fixed-tilt structures or to the roof of a building such as described in U.S. Pat. No. 6,111,189.
The PV module frame serves many other purposes. In addition to providing laminate edge protection and a means for mounting the PV module, the PV module frame provides a means to grip the PV module to carry and hold that during installation; the frame provides the appearance of a finished perimeter to the PV module; and the frame may be provided with a finish color to blend according to architectural requirements. In some cases, as in U.S. Pat. No. 6,111,189, the frame may provide means to conceal and protect the interconnection wiring in a PV array.
If the frame is made of a conducting material, the frame must be connected to a grounding conductor as a safety precaution in the event that the PV circuit within the PV laminate inadvertently develops an electrical short to the frame. The frame and the conductors and other electrical components and labor required for the grounding of the frame represent significant portions of the cost of the photovoltaic module. These cost elements are accentuated by the historical falling cost of the PV laminate, and represents a barrier to PV generated electricity achieving a cost that is competitive with conventional power sources. The frame typically increases the volume of a PV module, and this reduces the packing density and increases the cost of shipping the PV module. Also, in order to limit the number of product variations that a manufacturer must offer, PV module frames are typically designed such that a single frame design may be used in a variety of xe2x80x9ctypicalxe2x80x9d applications. As a result, the typical frame may not be suitable for applications that have very specific requirements. Manufacturers must therefore also develop custom frames for those applications, and this increases the manufacturer""s cost of operation and the PV module cost.
For these reasons, techniques have been investigated and developed to eliminate the requirement for frames for PV modules. In those cases, a variety of means have been developed to accommodate the attachment of the unframed PV laminate directly to a supporting surface.
In one example, as described in U.S. Pat. No. 5,143,556, mounting brackets are adhesively attached to the laminate back surface. The PV module is attached to the supporting structure by means of conventional fasteners engaging the clips and the supporting surface. This eliminates the cost of the frame and the requirement for grounding, but only partly increases the packing density. However, this introduces additional assembly and adhesive curing steps to the manufacturing process. The frameless PV module also specifically prescribes the required locations for the supporting structure members, and limits the number of attachments, thereby limiting the maximum allowable design pressure that the laminate may tolerate. This also imposes the requirement that the back side of the PV module be accessible during installation and module removal and replacement, which limits the application of this technique in typical building roof applications.
In another example, as described in U.S. Pat. No. 5,762,720, elements are bonded to the PV laminate back surface which elements can slidably engage the open side of a common electrical channel strut, including those marketed under the trademarks UNISTRUT(trademark) and BLINE(trademark). The method of the U.S. Pat. No. 5,762,720 has the advantages that no fasteners are required in order to attach the PV module to the supporting surface, that access is not required of the module back surface during installation, and that the requirement for grounding may be eliminated. One limitation of this technique is that if it becomes necessary to remove or replace only a single one of a number of PV modules that are slidably engaged to a supporting channel, it may be necessary to remove several of the adjacent PV modules as well. That limits the practicality of this technique, particularly in building roof applications. This technique also has the limitations described in the U.S. Pat. No. 5,143,556, above.
Another type of frameless PV module is described in U.S. Pat. No. 6,075,201, intended for use as a curtain wall or roof element.
Another approach pursued for attaching PV modules in building roof and other applications, has been to utilize conventional curtain wall, sloped glazing, skylight and other common building glazing materials and techniques. This approach typically employs conventional aluminum structural elements with glazing gaskets and cover caps. This has been shown to be particularly effective in building applications where the PV laminates are basically substituted for some or all of the conventional building glass or plastic glazing or other building panels, and where there is a significant requirement for weatherproofing the building exterior surfaces. This technique does not require special fixtures or clips permanently affixed to the module, as in U.S. Pat. Nos. 5,143,556 and 5,762,720. In addition, this technique accommodates the removal and replacement of single individual PV modules in an array of modules. However, the cost of such conventional building glazing materials and techniques cannot be economically justified in all PV applications, especially in those applications that do not have the rigorous architectural and weatherproofing requirements of building glazing, wall and roof elements.
The need that now exists is a low cost method for attaching a variety of unframed PV modules to a variety of supporting surfaces, including building surfaces, i.e., roofs and walls, where the applications do not impose strict architectural requirements or requirements for absolute weatherproofing. These applications include many non-building applications, as well as building rain screen architectural applications and building roof and wall applications where the PV modules are placed adjacent to or onto a finished waterproof building roof or wall surface.
Limited efforts have been undertaken to develop such methods for attaching a variety of unframed PV modules to a variety of supporting surfaces. There are a variety of common mounting clips and hardware widely used for other purposes that have self-evident applicability, and have been employed. These clips include those developed for attaching glass mirror panels and other panels to walls and to supporting surfaces. Some well-known clips have been employed for mounting glass mirror panels. Other clips have been developed for mounting other panels to walls and to other surfaces, for example, as described in U.S. Pat. Nos. 4,580,385 and 4,452,027.
The metal clips for surface mounting of glass mirror panels do not require access to the rear surface of the glass mirror panels. Such clips may incorporate flexible rubber cushion pads to protect the edge of the mirror panels and to spread the loads on the mirror back surface. Molded plastic clips function in a manner similar to the metal clip, except that cushions are not required owing to the softer nature of the plastic. The plastic clips may be free to rotate on their fastener, and depend on the clip contact with the edge of the glass mirror panel to properly align the clip to the glass mirror panel.
The clips in U.S. Pat. No. 4,580,385 were developed to accommodate the simultaneous attachment of two adjacent panels to a single supporting surface. Those also achieve attachment without the use of additional fasteners, by engaging a supporting surface consisting of a multiple-pierced hollow closed structural supporting element.
The clips in U.S. Pat. No. 4,452,027 accommodate the attachment of two adjacent panels, where the fastener mounting surface is depressed below the panel surface to accommodate the panel thickness. The clips in this patent also employs a rivet to attach the clip to the supporting element. Those clips align with the panel during installation by their contact with the edge of the attached panel.
Accordingly, the concepts described by these common mirror clips and glass panel clips have been adapted for employment in the mounting of PV modules, as will be described here.
U.S. Pat. No. 4,966,631 describes a xe2x80x9csupported photovoltaic arrayxe2x80x9d which includes the use of clips incorporating some of the features of the common clips. Those clips are mounted from the front of the PV module, and incorporate xe2x80x9ccushionsxe2x80x9d to protect the edge of the PV module and to spread the loads on the PV module back surface. Those clips become properly aligned to the PV module during installation by their contact with the edge of the attached PV module. The clips incorporate a fastener mounting surface that is depressed below the PV module surface to accommodate the PV module thickness.
The arrangement described in this U.S. Pat. No. 4,966,631 has a number of practical limitations.
Firstly, the cushioning pads do not protect the entire interface of the PV module back surface and the supporting surface. In practice, it is often the case that the surface of the structural elements is rough, and without a cushion at the entire interface the rough uncushioned surface of the support can easily damage the PV module back surface and/or lead to stress laminate concentrations that can damage the laminate elements including the laminate cells, electrical interconnections and the laminate back cover. Damage to the PV module back cover can lead to the PV module becoming electrically shorted to the support beam. This leads to a significant safety hazard.
Secondly, the PV module back surface contact with the structural element is not continuous and therefore does not offer complete support to the PV module against loads such as wind pressure impinging on the module front surface. As a result, with loads impinging on the PV module front surface, the PV laminate is allowed to deflect toward the supporting element. That leads to limitations in the maximum design load that the PV module may be exposed to from pressures acting on the PV module front surface.
Thirdly, in the design of U.S. Pat. No. 4,966,631, loads such as wind loads impinging on the PV module back surface are resisted only by these clips, which are acting only at discrete points on the PV module perimeter. This leads to high stress concentrations in the PV laminate front cover under certain loading conditions, and leads to limitations in the maximum design load that the PV module may be exposed to from loads acting on the PV module back surface.
Fourthly, during installation, the PV modules may not initially be placed without the clips in position. Therefore the clips must either be placed first, requiring that the clips be precisely pre-positioned, or that the clips and PV modules be placed simultaneously, which is an awkward maneuver for the installer. This is a particular limitation for building applications where the access to install the PV module may be difficult and awkward on account of the elevation and orientation of the building surface.
Fifth, removal and replacement of a single PV module attached with conventional fasteners would require free access to the space beneath the PV module. Removal and replacement of a PV module attached with rivets would require the awkward and difficult removal of rivets from a position above the PV module to be removed.
Sixth, the arrangement does not provide for the concealment or protection of electrical conductors beneath the PV modules.
Seventh, the clip in U.S. Pat. No. 4,966,631 does not provide a means to conceal the fasteners or other means to provide a more finished, attractive appearance to the clip installation.
Finally, the panels of PV modules mounted in this fashion, as shown in U.S. Pat. No. 4,966,631, have only limited stability against loads, including gravity loads, acting in the plane of the PV modules. This is a significant limitation, since it is common practice to depend on some xe2x80x9clateral stabilityxe2x80x9d sufficient to accommodate the assembly, transport and installation of panels of multiple PV modules. In this case, that stability is limited to that which is developed by the contact pressure developed at the discrete clip connection points. And that contact pressure can lead to stress concentrations in the PV module laminate and front and back covers. In addition, the panels of multiple PV modules may deflect laterally due to their insufficient xe2x80x9clateral stability.xe2x80x9d The structure can deform into a parallelogram, with the mounting clips being brought into closer contact with the PV module laminate edge on one side. This can lead to over-compression and failure of the clip cushion, and can lead to increased stress and mechanical contact between the clip and the laminate. It is well understood that nearly all failures of glass plates, regardless of the specific load condition, are initiated at the edge of the glass plate. As a result, in this instance, the increased stress and/or mechanical contact between the clip and the PV module glass front or rear cover can lead to the PV module failure at lower loads than would have otherwise been anticipated.
Consequently, none of the clips described hereinabove adequately address the requirements of a universal clip or attachment mechanism for the attachment of a variety of unframed PV modules to a various supporting surfaces.
Accordingly, it is the object of this invention to provide a means to attach unframed PV modules or other panels on a variety of supporting surfaces that avoids the limitations of the prior art.
It is another object of this invention to provide an attachment system that limits the stresses in the PV laminate that are induced when structural loads are applied to the PV module front and back surfaces.
It is another object of this invention to simplify the process of safely and expeditiously attaching, removing and replacing PV modules on a supporting surface.
It is yet another object of this invention to provide a means to conceal and protect the electrical conductors in an array of PV modules.
It is still another object of this invention to provide the means to provide lateral stability for a panel of multiple PV modules.
It is a further object of this invention to conceal the fasteners holding the clip in place, and to provide a more finished appearance to the installed clip.
In accordance with an important aspect of the present invention, a row of solar panels or similar panels can be formed using a system of clips, fasteners, glazing material and supporting beams.
In one possible preferred embodiment, the supporting beams may be channel-shaped, i.e., beams with one open slotted side, with the open or slotted side of the channel facing upward toward the back surface of the PV module. The supporting beams may be other shapes as well, including tubes and other common structural shapes such as rods, angles, wide-flange beams, etc. The supporting beams may be attached to the surface of a new or existing roof, or may be attached to any common tracking structure or fixed-tilt structure. When a channel supporting beam is used, the fasteners attaching the channel to the supporting structure or roof may be concealed in the channel beneath the PV module. In a roof application, sealant may be placed on the underside of a channel supporting beam, to facilitate the sealing and waterproofing of the fastener holes in the roof membrane. With the PV modules and clips in place, a channel supporting beam can provide a continuous enclosed space in contact with the PV laminate back surface. With the PV module appropriately positioned, the PV laminate conductors may exit the PV laminate into this space, and in any case the PV module and/or array conductors may be concealed and protected in this enclosed wireway.
A glazing material, such as 3M VHB Acrylic Foam Tape or butyl glazing tape, or equivalent, may be applied to the top surface(s) of the channel (or, equivalently, to the back surface of the PV module) to provide a continuous cushion between the supporting surface (e.g., the channel member) and the PV laminate rear surface. In addition, the glazing tape or equivalent may be supplied with adhesive characteristics that adheres the PV laminates in position during the installation process and before the clips are attached, and provides a fall or partial adhesive attachment of the PV laminate back surface to the supporting element to increase the allowable loads on the PV laminate back surface and the lateral stability of a panel of multiple PV modules.
In several preferred embodiments, the clips may be fabricated as injection molded plastic, however they may be fabricated by alternative methods and from alternative materials such as of extruded and/or machined aluminum, stamped or brake formed steel, etc. If plastic, the plastic material, such as GE Noryl, could be selected for the required strength, with (glass) fillers if necessary, and UV stabilized and electrically insulative properties. The clips may be developed to attach to the supporting beam top surface. In the preferred embodiment the clips may extend beyond the width of the supporting beam as necessary to reduce the stress in the PV laminate under loads impinging on the PV module bottom surface. The clips may be shaped with grooves or extensions that engage the supporting beam elements or edges. This will cause the clips to take the proper orientation without a PV module in place, and will restrain the walls of the channel from buckling laterally and from disengaging the fastener attaching the clip to the supporting beam channel.
In some preferred embodiments, the clips are attached to the channel supporting beam with fasteners and hardware that engage the channel elements such that the clips may be installed anywhere along the channel supporting beam, without providing special holes or receptacles.
In many preferred embodiments, during installation the PV modules may be securely placed and positioned temporarily on the adhesive glazing tape, and removed and repositioned if necessary. The clips are designed to be fastened in place with or without PV modules in position. This facilitates the initial installation of the PV modules. This also facilitates the removal and replacement of the PV modules in future, without having to disturb the adjacent PV modules. Access to the underside of the support structure is unnecessary.